<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script src="https://cdn.jsdelivr.net/npm/vue@2.5.17/dist/vue.js"></script>
</head>
<body>
<div id="app">
    姓：<input type="text" v-model= "msg"><br><br>
    名：<input type="text" v-model = "ming"><br><br>
    <input type="text" v-model="sd"><br>
    <div>{{fullName}}</div>
    <div>{{count}}</div>
    <div>{{ss}}</div>
    <div>你来自哪里</div>
    <select name="" id="" v-model="pro"> //在下拉框里是value值
        <option value="1">安徽</option>
        <option value="2">北京</option>
    </select>
</div>
<script>
   var vue = new Vue({
        el:'#app',
        data:{
            msg:'',
            ming:'',
            count:0,
            pro:'2',
            sd:""
        },
       computed: {
            fullName:function() {
                return this.msg + " " + this.ming;
            },
           ss:function () {
               return this.sd * 0.9;
           }
        },
        watch:{
          fullName:function () {
              this.count ++;
          }
        }
    });
</script>
</body>
</html>